The present invention relates to the field of control systems. More specifically, this invention relates to modular power control systems using pulse-width control modulators
FIG. 1 illustrates a conventional switching power module. As illustrated, an alternating (AC) voltage is input into power conversion module 110, which produces a direct (DC) output voltage, Vo. Output voltage, Vo, is input to feedback compensation control circuit 150, which monitors the value of output voltage Vo and adjusts the internal parameters of power conversion module 10 to maintain Vo relatively constant. The processing of feedback compensation control circuit 150 is well known in the art and may be implemented in special-purpose circuits, such a Field Programmable Gate Arrays (FPGAs) or Application Specific Integrated Circuits (ASICs).
The use of Application Specific Integrated Circuits to implement the control of power supplies is well known in the art. ASICs can perform the functions of a variety of discrete components on a single Integrated Circuit (IC). This is advantageous as the size of the controller and the overall size of the power supply can be reduced. Also, in large quantity, the cost of an ASIC is significantly less than the cost of discrete components that are required to perform the same functions. Hence, the overall cost and physical size of power supply units is reduced when ASIC technology is employed.
ASICs may be custom-made for the application or may be xe2x80x9coff-the-selfxe2x80x9d components. Custom-made ASICs are expensive and time-consuming to develop. Since the initial development cost for custom-made ASICs may be high, these devices are used in high volume applications. In such cases the development costs can be spread-out over the price of all the units sold. In addition, custom-made ASICs are typically designed to operate with a particular type of component or a component manufactured by a particular manufacturer.
Off-the-shelf ASICs are typically preprogrammed with known functions and require external devices, components or other hardware in order to use them in a designated application. The external components are necessary to interface the off-the-shelf ASIC to a particular device or component. The use of external components, however, is disadvantageous as their use increases the cost and the size of the power supply. A second disadvantage is that when the component is changed, the interface may also have to be changed, which consequently causes the ASIC to be changed.
One method of creating power supply controllers using off-the-shelf components to distribute processing among generic component blocks. The generic component blocks can consist of programmable micro-controllers that communicate operational commands to control devices, such as Pulse Width Modulators (PWM), over a data bus. Pulse Width Modulators are routinely included as peripherals in micro-controller based integrated circuits. Timing parameters, such as frequency, i.e., period, on-time, off-time, etc., which are used to control the output voltage level are stored in registers accessible by a micro-controller. Modularization of power supply controllers is disclosed in U.S. Pat. No. 6,157,093 and incorporated by reference herein.
FIG. 2 illustrates a conventional modular digital power supply controller 150 comprised of a master unit 200 and at least one slave unit 210a, 210b. As illustrated, master unit 200 is composed of processor 202, memory 204 and communication interface 206. Analog-to-digital (AID) converter 201 may optionally be included for conversion of analog signals to digital form for processing by processor 201. Slave units 210a, 210b are composed of communication interface 222, PWM generator 218, registers 212 and micro-controller or DSP 214. Analog-to-digital (A/D) converter 216 may optionally be included for conversion of analog signals to digital form for processing. PWM generators 218 are routinely included as peripherals in micro-controller integrated circuits. In such cases, timing parameters, e.g., frequency, on-time, off-time, etc., can be are stored in register 212. These values can be set in register 212 by local micro-controller 214 or remotely by processor 202 over communication link 208.
Remotely controlled operation of PWM is, however, limited because of bandwidth constraints. In voltage-mode control applications, the control of power module 150, of FIG. 1, by PWM 218 is in the order of few hundred or a few thousand hertz. In this case, the rate of updating the register content is relatively low, hence, the limited bandwidth of micro-controller 202, such as, 80C51-based micro-controllers, or data bus 208 is sufficient for updating the registers stored in slave unit 210a, for example. On the other hand, in current-mode control applications the PWM output is required to respond within a few hundred nanoseconds. Being bandwidth limited, the earlier described distributed power supply controller cannot respond within such a short time period. Hence, there is in a need in the art to provide a means for high-speed updating of pulse width modulator parameters that does not require expensive high-speed components and control signals.
A pulse width modulator (PWM) capable of exercising control signals in voltage-controlled, i.e., low-speed, and current-controlled, i.e., high-speed, power supply controllers is presented. The pulse width modulator, responsive to initial or slowly updated control signals can initiate control signals that provide either a slow-speed or high-speed changes. In one aspect of the invention, wherein the PWM is in communication with a relatively slow processor over a band-limited digital communication link, the PWM can be used to generate, an otherwise band-limited, control signal in response to a rapidly changing input signal. In this aspect of the invention, the modular construction of power supply controller provides a level of flexibility and interchangeability without incurring the cost of custom-made IC development.